@echo off
set "server_name=server_manager"
title %server_name%
set "var=test"
echo %var%

for /f "tokens=4" %%i in ('dir') do (
    echo %%i | findstr /C:%server_name% > nul
    if not errorlevel 1 (
        set "var=%%i"
    )
)

echo %var%

set "run_cmd=javaw  -Xms64m -Xmx128m -jar %var% server_manager.server"
echo %run_cmd%

%run_cmd%